Radiation imagery chemistry: process – composition – or product th – Imaged product – Structurally defined
Reexamination Certificate
1999-06-16
2001-04-03
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Structurally defined
C430S017000, C430S018000, C430S961000, C430S014000
Reexamination Certificate
active
06210844
ABSTRACT:
The invention relates to a protective layer on color proofs. More particularly, this invention relates to a protective polymeric layer for color proofs, a process for applying the protective layer on a color proof, and a color proof provided with a protective layer.
Screened color separations are used in reprography as copy originals for preparing offset or letterpress printing plates. Before the printing plates are exposed, the color separations are checked with the aid of color proofing processes for whether the subsequent printing result is a tonally accurate reproduction of the original.
Such color proofing processes use, for example, photosensitive recording materials with which the image is produced by using adhesion differences in the exposed and unexposed areas of the photosensitive layer. A positive-working reproduction process is disclosed in U.S. Pat. No. 3,649,268 in which a tacky photopolymerizable recording material is laminated on an image support and hardened by imagewise exposure. The exposed image areas lose their tackiness. The image can then be developed by applying colored particulate materials such as toners or pigments which selectively adhere to the unexposed tacky image areas. A negative-working process is described in U.S. Pat. No. 4,174,216 which teaches a negative-working element a support; a tacky, non-photosensitive contiguous layer; a photohardenable photoadherent layer; and a strippable cover sheet. After imagewise exposure to actinic radiation, the coversheet is peeled away, carrying with it the exposed areas of the photoadherent layer and revealing the tacky contiguous layer beneath. These tacky areas may then be toned with, for example, finely divided particulate material. Different colored layers can be prepared and assembled in register over one another to form multilayer color proofs, as is well know to those skilled in the art. U.S. Pat. No. 4,053,313 describes a similar negative-working system which is developed by solvent washout.
Other known photosensitive recording materials for preparing color proofs include precolored layers instead of tonable photosensitive layers, whereby the exposed material is developed by washoff with solvents as well as by peel-apart methods. The prior art also includes systems wherein the tackiness is increased by exposure to actinic radiation instead of being reduced as in the systems described above.
Color proofs are generally provided with an added protective layer to protect against mechanical and chemical interactions. For this purpose, a layer of a photopolymerizable material can be applied and polymerized overall, as described in U.S. Pat. No. 4,174,216. This process has the disadvantage that an additional exposure step is necessary. Further, there are various special protective layers of non-photosensitive materials. Double layer materials having an antiblocking layer and an adhesion layer are described in EP-B 0 242 655. Similarly, a combination of an actual protective layer of synthetic resin films and an adhesion layer is described in U.S. Pat. No. 4,329,420. Single layer materials are described in EP-B 0 285 039 and EP-B 0 365 355. According to EP-B 0 285 039, mixtures of special incompatible polymers are used. According to EP-B 0 365 355, thermoplastic resins having a Tg of 50 to 80° C. must be used.
The present invention is based on the problem of making available effective protection for color proofs against mechanical and chemical interactions, such protection having properties stable during storage of the color proofs at room temperature, without damaging the resolution or the tonal reproduction of the color proofs, or distorting the color images and without added processing steps or added auxiliary layers being required.
SUMMARY OF THE INVENTION
The present invention is directed to an element comprising a strippable support film and at least one protective layer including at least one polymer having a melting point Tin of at least about 50° C. and a glass transition temperature Tg of at most about 0° C. The element of the present invention is especially useful to provide a protective layer on proofs.
In another embodiment, the invention is directed to an article comprising an image disposed on at least one surface of a substrate, the image optionally comprising multiple color images, and a protective layer on the image-bearing surface of the substrate, characterized in that the protective layer includes at least one polymer having a melting point Tm of at least about 50° C. and a glass transition temperature Tg of at most about 0° C.
In still another embodiment, the invention is directed to a process for applying a protective layer on an image-bearing surface to form an article having an image disposed on at least one surface of a substrate, the image optionally comprising multiple color images, and a protective layer on the image-bearing surface of the substrate, characterized in that the protective layer includes at least one polymer having a melting point Tm of at least about 50° C. and a glass transition temperature Tg of at most about 0° C., the process comprising:
providing an element comprising a support film and a protective layer, the protective layer having a free surface and an opposing support surface adjacent the support film;
adhering the free surface of the protective layer to the image-bearing surface, the image-bearing surface optionally comprising multiple color images; and
removing the support film, whereby the protective layer is transferred onto the image bearing surface.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description of the preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Protective Element:
The element for application to an image-bearing surface comprises a strippable support film and at least one protective layer including at least one polymer having a melting point Tm of at least about 50° C. and a glass transition temperature Tg of at most about 0° C. Mixtures of polymers having the above characteristics may also be used in the non-photosensitive protective layer. In a preferred embodiment, the protective layer is transparent and non-photosensitive.
The protective element of this invention may be applied to many types of image-bearing surfaces. Some examples of image-bearing surfaces include Cromalin® proofs, Easyprint® proofs, etc.
The protective layer can be prepared by known methods. For this purpose, they can be coated on suitable supports from currently available solvents, preferably organic solvents, such as, for example, methylene chloride, toluene/methanol mixtures, or other mixtures of aromatic solvents and alcohols, esters, or ketones, and subsequently dried.
The thickness of the protective layer is usually about 1-20 &mgr;m, preferably about 3-15 &mgr;m, and particularly preferred at about 5-10 &mgr;m. A composite of two or more layers is also possible for this protective element. Two or more layers having the above specified thermoplastic polymers can be applied on the support successively or simultaneously by known methods. The layers of such multilayer protective elements can have the same or different compositions. Single-layer elements are preferred.
Polymer:
Useful polymers have a melting point Tm of at least about 50° C. and a glass transition temperature of at most about 0° C. Preferred polymers have a melting point Tm of about 50-120° C., particularly about 50-100° C., and a glass transition temperature Tg of at most about −20° C., particularly at most about −40° C. Suitable polymers include, for example, polyethylene oxides, polypropylene oxides, polytetrahydrofurans, polycaprolactones and combinations thereof. Polycaprolactones, polyethylene oxides and polypropylene oxides are particularly preferred, especially polycaprolactones. The polymer is present in the amount of from about 80 to about 100% by weight, preferably from about 90 to about 100% by weight, based on the total weight of the layer.
Additives:
Baxter Janet
E. I. Du Pont de Nemours and Company
Walke Amanda C.
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